The present invention relates to the fitment of the bead area or profile of a pneumatic tire relative to the rim flange to which the tire is to be mounted, more particularly the invention relates to an improved method of profiling this portion of the tire""s bead.
Historically, with the introduction of the tubeless type tire, the fitment of the bead portions of the tire to the design rim has increased in significance. This fitment insures that the tire remains air tightly sealed and securely fixed to the rim during vehicle use.
The typical rim has a ledge and a flange that define the contact zone with the tire bead. The tire bead has a first annular surface between the bead heel and bead toe that upon assembly to the rim contacts the rim ledge. The bead also has a second annular surface radially outward of the bead heel. This annular surface contacts the rim flange when the tire is mounted and inflated on the rim.
The prior art teaches the use of a rim with a cylindrical or very slightly conical ledge. Typically for a passenger tire the rim ledge was inclined at an angle of 5xc2x0 relative to the axis of rotation of the tire. To ensure a proper fitment, the tire beads had an annular surface having a similar 5xc2x0 inclination relative to the axis of rotation, the beads having a slightly smaller diameter than the rim ledge, thus upon assembly, an interference fit would be achieved.
As a later development, the radially innermost flexible portion of the tire between the toe and the annular tensile member comprised an inclined surface about 10xc2x0 or 5xc2x0 greater than the rim ledge. This added interference created by the angular variation facilitated sealing the tire.
Typically the portion of the bead""s second annular surface adjacent the heel and the matching portion of the rim flange are at 90xc2x0 relative to the wheel axis. This annular surface area being under pressure while the tire is inflated contacts the rim flange, helping to fasten the tire on the rim.
The prior art tires essentially relied on the rim ledge and flange orientation to establish the shape and orientation of the bead, with the exception being the flexible toe portion of the bead.
Generally, the optimal bead fitment relationship occurs when the tire bead profile exactly fits the rim profile with no gaps. Quite often, however, there is a separation between the tire and the rim in the heel-to-flange region. This gap or separation can occur around the entire peripheral surface or it may be locally occurring with the rim flange and tire bead sporadically making contact.
In either case the gap in the flange region provides no assistance to the tire""s resistance to rim slippage. Often the gap is caused by the rotation of the bead upon tire inflation and mounting due to a nonuniform tire-rim interference along the rim ledge and unequal cord tension on the two sides of the bead core.
Ideally the tire when mounted to its design rim will fit flush against the rim flange. A poor fitment in the flange area can cause the bead seat profile of the tire to seat axially inward of the design location, thus lowering the amount of contact pressure that should be generated under the bead core.
In U.S. Pat. No. 5,445,202 assigned to The Goodyear Tire and Rubber Company the second annular surface extending radially outward along the rim flange region was inclined at an angle at least 3xc2x0 relative to the rim flange. This allowed the bead to rotate as the tire is mounted to enable the second surface to contact the rim flange without obstructing the bead seat profile from fully engaging the rim ledge.
In another Goodyear patent, U.S. Pat. No. 5,464,051, the inclination of this second annular surface was recommended to be in the range of 0xc2x0 to 3xc2x0 relative to the rim flange.
In U.S. Pat. No. 5,332,019 to Yoshida et al a similar observation was made relating to the rim flange gap being the result of an attempt to overlap the profile of bead portions in the region of the bead seat and the flange. Yoshida et al used an x-ray CT scanner to study its effect and found that while the bottom of the bead contacts the rim airtightly a gap formed between side face of the bead portion and the axially inner surface of the rim flange results in the tire having an increase in Radial Runout (RRO) and Force Variation (FV). To solve the problem and provide improved contact between the bead portions and the mating surfaces of the rim, Yoshida et al discloses a special profile based on a mathematical formula. In a cross-section including the tire axis, the bead profile is within a range between a locus of y=f(x)+1(mm) and f(x)xe2x88x921(mm) which are made when x-value is varied from 15.29 to 0.523 (mm) wherein f(x)=3.789+2.4273 x+0.73024 x2+0.12736 x3+0.012774 x4+6.659xc3x9710xe2x88x924 x5+1.36xc3x9710xe2x88x925 x6. In the above, f(x) is a function of x, and x and y are the radial and the axial coordinates respectively in millimeters, defining the direction of increase of the x value as being radially inward and the direction of increase of the y-value as being axially inward of the tire. The origin of the x and y coordinates is the bead""s sharp point, which is the intersecting point between the straight bead bottom line being inclined at 5 degrees to the tires axis and the straight bead side line parallel to the tire radial direction.
As can be readily appreciated, the problem has been clearly observed by those of skill in the art of tire design and the solutions vary from simplistic to Yoshida""s overwhelmingly complex equation with a plus or minus 1 mm variation thus yielding an almost nondecernable profile. In addition, the solution in one case may not be applicable to another because of differences in the bead core, the wrapped-around reinforcing cords, and the bead seat profile resulting in a different bead rotation.
It is an object of the present invention to predict or measure the amount of bead rotation that will occur while a particular tire construction is mounted to its design rim, and to revise the bead flange profile with the anticipated rotation so that after mounting and inflation the tire will fit the rim. The method of bead flange profiling described herein has general applications regardless of the other design aspects of a bead, such as the type and construction of bead core and the type of bead seat profile.
The method of designing a bead flange profile for a pneumatic tire to be mounted on a design rim as specified for the tire size has the steps of (a) selecting a design rim and a cured tire construction and bead profile; (b) predicting or measuring the tire deformation upon mounting and inflation, (c) analyzing the deformation to show the compressed beat seat profile and the bead flange profile contacting the rim flange from a preselected radially outer point C extending radially inwardly toward the bead heel of the tire; (d) identifying any gaps between the tire and the rim; (e) modifying the tire""s bead flange profile to eliminate any gaps by moving selected points on the bead profile in proportion to the local gap sizes; (f) shifting all the points modified in step (e) axially inward by a distance so that the axially outermost position of the modified profile is the same as the axially outermost position of the original profile; and then (g) smoothing the connections of the modified portion of the bead profile to the rest of the bead profile up to the radially outer contact with the rim flange.
The engineer can then preferably take the adjusted flange profile of step (g) and repeat the steps (a) through (g) to verify no additional gaps exist. If new or additional gaps are found, the steps should be repeated until the analysis predicts no gaps exist between the rim flange and the bead flange profile.
If the engineer wants to, he or she may elect to change the bead core construction, component gauges in the bead area, or the bead seat profile from a first design to a modified or otherwise changed second design, and repeat steps (a) through (g) to accomplish a gap-free fit relationship.
Definitions
xe2x80x9cAspect ratioxe2x80x9d of the tire means the ratio of its section height (SH) to its section width (SW) multiplied by 100% for expression as a percentage.
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d means lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cBeadxe2x80x9d means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chaffers, to fit the design rim.
xe2x80x9cBelt structurexe2x80x9d or xe2x80x9cReinforcing Beltsxe2x80x9d means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17 degrees to 27 degrees with respect to the equatorial plane of the tire.
xe2x80x9cCarcassxe2x80x9d means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
xe2x80x9cCordxe2x80x9d means one of the reinforcement strands of which the plies in the tire are comprised.
xe2x80x9cDesign rimxe2x80x9d means a rim having a specified configuration and width. For the purposes of this Specification, the design rim and design rim width are as specified by the industry standards in effect in the location in which the tire is made. For example, in the United States, the design rim is as specified by the Tire and Rim Association. In Europe, the rim is as specified in the European Tyre and Rim Technical Organisationxe2x80x94Standards Manual and the term design rim means the same as the standard measurement rims. In Japan, the standard organization is The Japan Automobile Tire Manufacturer""s Association.
xe2x80x9cEquatorial plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cInnerlinerxe2x80x9d means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire.
xe2x80x9cNormal inflation pressurexe2x80x9d refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cNormal loadxe2x80x9d refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cPlyxe2x80x9d means a continuous layer of rubber-coated parallel cords.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d means directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cRadial-ply tirexe2x80x9d means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65xc2x0 and 90xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cSection heightxe2x80x9d (SH) means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.
xe2x80x9cSection widthxe2x80x9d (SW) means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.
xe2x80x9cShoulderxe2x80x9d means the upper portion of a sidewall just below the tread edge.
xe2x80x9cSidewallxe2x80x9d means that portion of a tire between the tread and the bead.
xe2x80x9cTread widthxe2x80x9d means the arc length of the tread surface in the axial direction, that is, in a plane passing through the axis of rotation of the tire.